A friction lock electrical header which is sold under part number 640456 by AMP Incorporated of Harrisburg, Pa. comprises a plastic housing which holds contact posts that extend from opposite mating faces of the housing. Portions of the contact posts extending from one mating face can be soldered to plated through-holes in a circuit board. The housing itself is allowed to rest on the board but does not get directly attached to the board. Portions of the contact posts extending from the other mating face are matable with contacts of a mating connector. The header has a friction lock wall for securing the mating connector thereto, and force must be applied to the mating connector in order to overcome the friction lock during unmating of the connector from the header. During the unmating, considerable force is transferred to the header by the friction lock, and this force may pull the header housing off of the posts if the housing does not firmly grip the posts. The posts are interference fitted in cavities in the housing, and the interference fit has generally provided a sufficient post retention force. A problem arises when the header is subjected to high temperatures such as occur during surface mount solder reflow assembly processes. The high temperature causes a relaxation of the forces generated by the interference fit. In order to compensate for the relaxation, the amount of initial interference fit must be increased so that a sufficient post retention force remains after the solder reflow process. However, increasing the interference fit can result in cracks in the housing around the contact posts and an accompanying loss of retention force. There is a need for an inexpensive solution to this problem.